Experimental and detailed kinetic modeling of nitric oxide reduction by a natural gas blend in simulated reburning conditions

The reduction of nitric oxide (NO) in simulated conditions of the reburning zone has been studied in a fused silica jet-stirred reactor operating at atmospheric pressure, in the temperature range 1100-1500 K, in diluted conditions. A mixture of CH4 and C2H6 (10:1), a natural gas blend, was used as reburning fuel. The initial mole fractions of NO, hydrocarbon and H2O have been varied as well as the temperature, and the equivalence ratio. From the present study it was demonstrated that the NO reduction potential varies as the temperature, the initial mole fraction of reburning fuel, and that the initial mole fraction of NO has only a minor effect on the reduction of NO when the reduction of NO is high. In conditions where the reduction of NO is low, the efficiency of the process tends to moderately increase with the initial concentration of NO. Optimal conditions for the reburning of NO can be obtained for particular combinations of equivalence ratio and temperature. These results, which clarify the influence of these important parameters on the kinetics of NO reburning, are generally in agreement with previous investigations. A detailed chemical kinetic modeling of the present experiments was performed (786 reversible reactions and 113 species). An overall reasonable agreement between the present data and the modeling was obtained although improvements of the model are still needed. The main route to NO reduction involves ketenyl radical. The model indicates that the reaction path: HCCO + NO --> HCNO + CO followed by HCNO + H --> HCN + OH is responsible for the occurrence of a minima for TFN at phi similar or equal to 1.25. According to the present modeling, the reduction of NO by CH4/C2H6 mix can be summarized as: HCCO + NO --> HCNO -->, HCN --> NCO -->,HNCO --> NHi; NHi + NO --> N-2; NH + NO --> N2O; N2O + M,H --> N-2.